1. Field of the Invention
This invention relates to a process for the encapsulation of minute droplets of water-insoluble liquids (hereinafter referred to as oils).
2. Description of the Prior Art
Microcapsules containing both liquid and solid nucleus materials have found widespread acceptance in a variety of commercial applications. For example, one of the most widespread uses has been in the art of transfer-copy systems wherein minute droplets of a colourless dye intermediate dispersed or dissolved in an oil are encapsulated and coated onto a transfer sheet. The dye intermediarte is thereafter transferred to a copy sheet by rupturing the capsules by the application of a marking instrument. The underlying copy sheet has an adsorbent coating containing a material which will react with the dye intermediate causing a visible coloured mark at points where the microcapsules have been ruptured and the dye transferred. Other recent applications in which microcapsules have been used extensively are in adhesives and adhesive tapes, fertilizers, pharmaceuticals, foods and cosmetics.
Various techniques for the encapsulation of oil droplets have been proposed. U.S. Pat. No. 4,001,140 exemplifies recent technology in this art. Probably the most widely employed encapsulating material is gelatin, and the process by which it is utilised involves the phenomenon known as coacervation, which is exhibited by gelatin and certain other natural and synthetic polymeric materials which form colloidal solutions in water.
One of the disadvantages of the coacervation encapsulation techniques is that critical control over the concentrations of the colloidal material and the coacervation initiator must be maintained. In addition, when a gelable colloid such as gelatin, is used as the encapsulating material, coacervation must take place at a temperature above the gel point of the colloid.
The process of the present invention does not involve the coacervation phenomenon, the disadvantages of which are therefore avoided.